Insights into the role of β-MnO2 and oxalic acid complex expediting ozonation: Structural properties and mechanism

The complexation between metal oxides and organic acid plays an important role in the water treatment. However, the mechanism of complex in catalytic ozonation process (HCO) has not been studied yet. In this study, a β-MnO2-oxalic acid (β-MnO2-OA) complex was constructed and used in HCO for pCBA degradation (β-MnO2/OA/O3). The addition of OA enhanced not only k value of β-MnO2/OA/O3 process by 4 times that of ozonation alone, but also had advantageous effects on co-degradation of contaminant and OA. The 90.4 % of pCBA and 65.2 % of OA degradation were achieved at pH 4.0 within 10 mins by the incorporation of OA (10 mg/L) and β-MnO2 (50 mg/L). Systematic characterization techniques (XPS, H2-TPR, and etc.) confirmed the enhanced electron transfer ability and redox property of β-MnO2-OA complex. More oxygen vacancies and reactive oxygen species (ROS) were generated through facilitating oxygen species migration. Besides, sodium pyrophosphate tests demonstrated that Mn3+ was mainly responsible for the formation of β-MnO2-OA complex. Scavenger experiments identified surface-•OH and liquid-•OH as major reactive radicals for pCBA degradation, while other ROS were the radicals involved in OA removal. Finally, a feasible mechanism involving solid–liquid interface reaction was elaborated, which presented a potential strategy improving catalytic ozonation performance.